Cap-sensitive self-supporting explosive with crosslinked thermoset resin binder

ABSTRACT

STIFF, TOUGH, LOW-EXOTHERM FORMULATED SELF-SUPPORTING CAP-SENSITIVE EXPLOSIVE COMPOSITION COMPRISING A MIXTURE OF CAP-SENSITIVE HIGH EXPLOSIVE AND CROSSLINKED THERMOSET RESIN BINDER COMPRISING EITHER (A) THE CROSSLINKED REACTION PRODUCT OF LIQUID ISOCYANATE TERMINATED POLYURETHANE AND NITROCELLULOSE OR (B) THE CROSSLINKED REACTION PRODUCT OF LIQUID EPOXY RESIN AND LIQUID PHENOL-FORMALDEHYDE RESIN.

United States Patent O 3,554,820 CAP-SENSITIVE SELF-SUPPORTING EXPLOSIVE WITH CROSSLINKED THERMOSET RESIN BINDER William L. Evans, Blackwood, N.J., assiguor to E. I. du Pout de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Filed Aug. 27, 1968, Ser. No. 755,722 Int. Cl. F42b 1/00; C06b 3/00, 7/00 US. Cl. 149-19 13 Claims ABSTRACT OF THE DISCLOSURE Stiff, tough, low-exotherm formulated self-supporting cap-sensitive explosive composition comprising a mixture of cap-sensitive high explosive and crosslinked thermoset resin binder comprising either (a) the crosslinked reaction product of liquid isocyanate terminated polyurethane and nitrocellulose or (b) the crosslinked reaction product of liquid epoxy resin and liquid phenol-formaldehyde resin.

BACKGROUND OF THE INVENTION Flexible cap-sensitive self-supporting explosive compositions have found wide application in the explosives art. Such flexible explosive compositions have been developed by the incorporation of various flexible and rubbery materials in the binder composition. However, there is now a need for a stiff, tough, self-supporting cap-sensitive explosive composition for use in military applications, and for primers, capshells and other structural uses.

Past attempts at developing stiff, tough, self-supporting explosive compositions have not been successful due to unsafe exotherms being produced upon curing.

SUMMARY OF THE INVENTION In accordance with this invention, there is provided a stiff, tough, solvent-resistant, self-supporting, cap-sensitive explosive composition with good thermal stability, which is easily made from available raw materials with no unsafe exotherms during formulation and which can be molded, extruded, cast, rolled, pressed or stamped from sheets into special shapes. The explosive composition is especially useful as a sheet explosive.

More specifically this invention provides an explosive composition which comprises a mixture of about from 50 to 85 percent of a cap-sensitive high explosive and about from 15 to 50 percent crosslinked thermoset resin binder comprising the crosslinked reaction product .of either polyurethane and nitrocellulose in the weight ratio of about from :1 to 3:1 or liquid epoxy resin and liquid phenol-formaldehyde resin in the weight ratio of about from 1:5 to 5:1.

DESCRIPTION OF I PREFERRED EMBODIMENTS Any cap-sensitive high explosive is suitable for use in this invention. As used in this invention, cap-sensitve high explosive is meant to include a single cap-sensitive high explosive, a mixture of two or more cap-sensitive high explosives and mixtures of one or more cap-sensitive high explosives with one or more other high explosives, e.g., trinitrotoluene or ammonium nitrate, the mixture being cap-sensitive, i.e., sensitive to initiation by a No. 8 blasting cap.

. Especially suitable for use in this invention are capsensitive high explosive organic nitrates, nitramines and aromatic nitro compounds.

Examples of specific cap-sensitive high explosive compounds that can be used in this invention include pentaerythritol tetranitrate (PETN), bis(trinitroethyl)urea, ammonium picrate, 2,4,6-trinitrophenyl methylnitramine (Tetryl), potassium dinitroacetonitrile, cyclotrimethylice enetrinitramine ,(RDX), cyclotetramethylenetetranitramine (HMX), tetranitrodibenzo-l,3a,4,6a-tetra-azopentalene (including all its isomers based on the various positions of the nitro groups), lead azide, mannitol hexanitrate, diazidodinitrophenol, hexamethylene triperoxydiamine, picrylsulfone and mixtures thereof. RDX, HMX and especially PETN have optimum properties for use in this invention and are accordingly preferred.

The cap-sensitive high explosive constitutes about from 50 to 85 percent of the final composition. If substantially greater amounts of the explosive component are utilized, the final compositions lack the desired degree of cohesiveness, whereas the use of substantially lesser amounts of the high explosive results in products which have unreliable detonation characteristics. An optimum balance ofexplosive characteristics and physical properties has been found to be present in the final explosive compositions when the high explosive component is from about 50 to 70 percent of the total weight. Accordingly, this latter concentration range is preferred in the instant explosive compositions.

The particle size of the high explosive is not critical, although particles which pass an SO-mesh US. Standard sieve are preferred, and especially preferred are particles whose average major dimension does not exceed 100 microns. The latter are described as superfine explosives. In addition, the explosive compositions are more sensitive to initiation if the high explosive particles are prepared by the process of mixing a solution of the explosive with a non-solvent, which is miscible with the solvent, in a jet-impingement mixer, such as the process disclosed in Canadian Pat. 533,487.

The binder in the instant invention is a cross-linked thermoset resin and constitutes from about 15 to 50 percent of the final composition. In line with the preferred concentration range of the high explosive, the preferred concentration range of the binder is about from 30 to 50 percent of the final composition.

The crosslinked thermoset resin used in the instant invention is the crosslinked reaction product of either liquid polyurethane and nitrocellulose or liquid epoxy resin and liquid phenol-formaldehyde resin. The polyurethane to nitrocellulose weight ratio should be from about 20:1 to 3:1, preferably from about 14:1 to 3:1.

Any liquid polyurethane which has terminal isocyanate groups, by which it can be cured to form a solid elastomer, is suitable for use in this invention. In general, polyurethanes may be described as the reaction products of dior polyisocyanates and bi-or polyfunctional alcohols, including polyesters and polyethers. (When polyesters or I polyethers are used, the resulting polyurethanes are known as polyester urethanes and polyether urethanes, respectively.)

Any of a wide variety of dior polyisocyanates may be used in this reaction, including aromatic, aliphatic and cycloaliphatic dior polyisocyanates and combinations of these types. Representative compounds include 2,4- tolylene diisocyanate, 1,6-hexamethylene diisocyanate, 1,5-naphthalene diisocyanate, 4,4-diphenyldiisocyanate, 4,4'-diphenylmethane diisocyanate, 1,4-phenylene diisocyanate and mixtures thereof.

Similarly, a wide variety of bior polyfunctional alcohols may be used such as the hydroxy terminated polyesters and polyethers. Representative examples include 1,2-polydimethylene ether glycol, polydecamethylene ether glycol, polyethylene glycol dibenzoate, polytetramethylene ether glycol, butanedio1-1,3, polypropylene ether glycol, and mixtures thereof.

Particularly suitable for use in this invention are the liquid isocyanate terminated polyether urethanes, such as, for example, Adiprenes L-lOO, L-167, L-315 and L 420, which are manufactured by E. I. du Pont de Nemours 3 & Co. Especially preferred are Adiprenes L-100 and L-315.

Such liquid polyether urethanes sometimes are designated as prepolymers or intermediate polymers because on reaction with curing agents they are cured or vulcanized to form solid elastomers.

The liquid polyurethane is cured by the nitrocellulose. As long as free hydroxy groups are available, any nitrocellulose is suitable for this invention. Although viscosity is not critical, high viscosity types are preferred since stiff products are desired.

The epoxy-resin to phenol-formaldehyde ratio should be from about 1:5 to 5:1, preferably from about 1:2 to 2:1.

Any liquid epoxy resin is suitable for use in this invention. Epoxy resins are thermosetting resins. The thermosetting characteristics is based on the reactivity of the epoxide group,

In genreal, the more common epoxy resins can be described as the reaction products of epoxy compounds, such as 1,2-epoxypropane, 1,2-epoxybutane, 2,3-epoxybutane and epichlorohydrin, and dihydric phenols, such as catechol, resorcinol and p,p'-isopropylidenediphenol (Bisphenol A).

Particularly suitable for use in this invention are the liquid epoxy resin condensation products of epichlorohydrin and Bisphenol A, such as, for example, those available from the Shell Chemical Co. as Epon resins. Liquid Epon resins which have an epoxide equivalent of about from 140 to 190 grams and a weight per gallon of about from 9.7 to 10.2 pounds, such as Epons 812, 820, 826 and 828, are preferred. Especially preferred are Epons 812 and 828.

The liquid epoxy resin is cured by liquid phenolformaldehyde resin, and any liquid phenol-formaldehyde resin is suitable for this use. Phenol-formaldehyde resins are thermosetting plastics and, in general, can be described as the reaction products of phenol and formaldehyde.

Particularly suitable for use in this invention are the liquid phenol-formaldehyde resins available from the Union Carbide Corporation as BRLs. BRLs which are heat reactive liquid phenol-formaldehyde resins with viscosities of about from 275 to 80,000 centipoises, such as BRLs 1251, 1373 and 2028, are preferred.

The explosive compositions of this invention can be prepared by uniformly blending the components, fashioning the resulting putty-like mass into desired shapes, and then curing the resulting products to yield the desired stiff products. More specifically, the explosive compositions can be prepared by charging the ingredients into a mixer and, while circulating cold water through a jacket, mixing for about from one-half hour to two hours until a homogeneous putty-like mass is formed, under reduced pressure. Although reduced pressure is not a limiting factor, reduced pressure tends to reduce the entrapment of air bubbles in the composition, thereby making it tougher. The putty-like mass is removed from the mixer and is then molded, extruded, cast, rolled, pressed, stamped or otherwise fashioned into desired shapes.

It is then cured at room temperature or at elevated temperatures, preferably about from 150 to 200 F. The elevated temperatures accelerate the curing process.

Curing takes about from to 72 hours but can be accelerated to about from two to four hours by the addition of crosslinking accelerators, such as dibutyltin dilaurate, in amounts of from about 0.1 to 0.2 percent. When accelerators are used, they are added at the initial blending stage of the ingredients. No unsafe exotherm is produced upon curing.

The cured product is stiff, tough and solvent resistant. It is detonated by conventional blasting caps, typical detonation velocities being on the order at about from 6000 to 7500 meters per second. Finally, it has good thermal stability in temperatures of up to about 250 F.

Optionally, various additives may be incorporated into the composition to slightly modify the physical properties. For instance, small amounts of plasticizers, such as acetyl tributyl citrate, may be added in amounts of about from 0 to 5% to add some flexibility to the final composition. Pigments and dyes may be added in small amounts to affect coloration. Finally, small amounts of fillers, such as fibers, metal powders and powdered solids can be added to modify the rigidity and conductivity of the compositions.

The following examples provide further specific illustrations of the explosive compositions of this invention. In the examples, parts and percentages reported are by weight.

EXAMPLE 1 70.0 parts of superfine PETN, 23.0 parts of Adiprene L-315 7.0 parts of high viscosity nitrocellulose, having a nitrogen content of about from 12.15 to about 12.35 percent and a degree of polymerization of around 810, and 01- part dibutyltin dilaurate are charged into a mixer and, while cold water is circulated through a jacket, mixed for about one-half hour, with vacuum being applied the last 10 minutes. The putty-like mass is removed from the mixer and pressed to A;-inch sheets between release paper and cured for about 15 hours at room temperature. No unsafe exotherm is produced during curing.

The cured product is stiff, tough and solvent resistant. It has good thermal stability when heated at 250 F. for 24 hours. It is detonated with a conventional blasting cap with base charge of 0.3 grain of HMX.

EXAMPLE 2 Following the general procedure of Example 1, a composition is prepared of 70.0 parts of superfine PETN, 23.0 parts of Adiprene L-100 7.0 parts of high viscosity nitrocellulose, having a nitrogen content of about from 10.9 to 11.2 percent and a degree of polymerization of around 275, and 0.2 part of dibutyltin dilaurate. The sheets are cured for about two hours at 200 F. No -unsafe exotherm is produced during curing.

The cured product is from stiff to very slightly flexible, tough and solvent resistant. It has good thermal stability when heated at 250 F. for 24 hours. It is detonated with a conventional blasting cap with base charge of 4.9 grains of PETN.

EXAMPLE 3 Following the general procedure of Example 1, a composition is prepared of 60.0 parts of superfine PETN, 30.0 parts of Adiprene L-100 and 10.0 parts of high viscosity nitrocellulose, having a nitrogen content of about from 12.15 to 12.35 percent and a degree of polymerization of around 810. The sheets are cured for about 72 hours at room temperature. No unsafe exotherm is produced during curing.

The cured product is very stiff, tough and solvent resistant. It has good thermal stability when heated at 225 F. for 22 hours. It is detonated with a conventional blasting cap with base charge of 2 grains of PETN.

EXAMPLE 4 Following the general procedure of Example 1, a composition is prepared of 65.0 parts of superfine PETN, 27.0 parts of Adiprene L-315. 8.0 parts of high viscosity nitrocellulose, having a nitrogen content of about 1 Adipreue 13-315 is a liquid polyether urethane which is made by reacting one mol of PTMEG of number average molecular Weight about 1000, one mol of butanediol 1,3, and about four mols of mixed tolylene diisocyanate isomers for four hours at C. under nitrogen, as disclosed in U.S. Pat. No. 3,188,302.

2 Adiprene L- is a liquid polyether urethane which is made by reacting one mol of polytetramethylene ether glycol (P'lMEG) of number average molecular weight about 1000 with about 1.6 mols of mixed tolylene diisocyanates, as disclosed, for example, in U.S. Pats. Nos. 2,929,800 or 2,948,601.

from 12.15 to 12.35 percent and a degree of polymerization of around 810, and 0.2 part of dibutyltin dilaurate. The sheets are cured at 200 F. for about two hours. No unsafe exotherm is produced during curing.

The cured product is stiff, tough and solvent resistant. It has good thermal stability when heated at 250 F. for 24 hours. It is detonated with a conventional blasting cap with base charge of 4.9 grains of PETN.

EXAMPLE Following the general procedure of Example 1, a composition is prepared of 60.0 parts of superfine PETN, 15.0 parts of Epon 828 5.0 parts of Epon 812 and 20.0 parts of BRL 2028 The sheets are cured at 150 F. for 17 hours. No unsafe exotherm is produced during curing.

The cured product is stiif, tough and solvent resistant. It has good thermal stability when heated at 225 F. for 22 hours. It is detonated with a conventional blasting cap with base charge of 4.9 grains of PETN.

EXAMPLE 6 Following the general procedure of Example 1, a composition is prepared of 60.0 parts of PETN, 25.0 parts of Epon 812 and .0 parts of BRL 2028. The sheets are cured at 150 F. for 17 hours. No unsafe exotherm is produced during curing.

The cured product is from stiff to very slightly flexible, tough and solvent resistant. It has good thermal stability when heated at 225 F. for 22 hours. It is detonated with a conventional blasting cap with base charge of 2.0 grains of PETN.

EXAMPLE 7 Following the general procedure of Example 1, a composition is prepared of 60.0 parts of PETN, 15.0 parts of Epon 828, 5.0 parts of Epon 812 and 15.0 parts of BRL 1373 The sheets are cured at 150 F. for 24 hours. No unsafe exotherm is produced during curing.

The cured product is stiif, tough and solvent resistant. It has good thermal stability when heated at 225 F. for 24 hours. It is detonated with a conventional blasting cap with base charge of 2.0 grains of PETN.

What is claimed is:

1. A stiff, tough, self-supporting explosive composition comprising a mixture of about from 50 to 85 percent of 3 "Epon 828 is a liquid epoxy resin condensation product of epichlorohydrin and Bisphenol A having a. viscosity of from 100 to 160 poises, a. refractive index at C. of 1.573, a Weight per gallon of 917 pounds, and an epoxide equivalent of from 180 to 195, epoxide equivalent being the number of grams of resin containing one gram-equivalent of epoxide.

4 Epon 812 is a liquid epoxy resin condensation product of epichlorohydrin and Bisphenol A having a. viscosity of from C to F on the Gardner-Holdt scale, a refractive index at 25 C. of 1.478, a. weight per gallon of 10.2 pounds, and an epoxide equivalent of from 140 to 160.

5 BRL 2028 is a liquid heat-reactive phenol formaldehyde resin available from the Union Carbide Corporation with a viscosity at 25 C. of from 35,000 to 80,000 centipoises.

BRL 1373 is a. liquid heat-reactive phenol-formaldehyde resin available from the Union Carbide Corporation with a viscosity at 25 C. of from 400 to 650 centipoisesand a specific gravity at 25 C. of from 1.191 to 1.199 grams per cubic centimeter.

cap-sensitive high explosive and about from 15 to 50 percent crosslinked thermoset resin binder comprising one of the group consisting of (a) the crosslinked reaction product of liquid isocyanate terminated polyurethane and nitrocellulose in the weight ratio of about from 20:1 to 3:1, respectively, and (b) the crosslinked reaction product of liquid epoxy resin and liquid phenol-formaldehyde resin in the weight ratio of about from 1:5 to 5:1, respectively.

2. An explosive composition of claim 1 wherein said cap-sensitive high explosive comprises at least one of the group consisting of pentaerythritol tetranitrate, cyclotrimethylenetrinitramine, cyclotetramethylaminetetranitramine, and mixtures thereof with trinitrotoluene.

3. An explosive composition of claim 2 wherein said crosslinked thermoset resin binder comprises the crosslinked reaction product of liquid isocyanate terminated polyurethane and nitrocellulose.

4. An explosive composition of claim 3 wherein said polyurethane is polyether urethane.

5. An explosive composition of claim 4 wherein said polyether urethane and nitrocellulose are in the weight ratio of about from 14:1 to 3:1, respectively.

6. An explosive composition of claim 5 which comprises a mixture of about from 50 to percent of said cap-sensitive high explosive and about from 30 to 50 percent of said crosslinked thermoset resin binder.

7. An explosive composition of claim 6 wherein said cap-sensitive high explosive is pentaerythritol tetranitrate.

8. An explosive composition of claim 2 wherein said crosslinked thermoset resin binder comprises the crosslinked reaction product of liquid epoxy resin and liquid phenol-formaldehyde resin.

9. An explosive composition of claim 8 wherein said epoxy resin is a condensation product of epichlorohydrin and p,p-isopropylidenediphenol.

10. An explosive composition of claim 9 wherein said epoxy resin and phenol-formaldehyde resin are in the weight ratio of about from 1:2 to 2:1, respectively.

11. An explosive composition of claim 10 which comprises a mixture of about from 50 to 70 percent of said cap-sensitive high explosive and about from 30 to 50 percent of said crosslinked thermoset resin binder.

12. An explosive composition of claim 11 wherein said cap-sensitive high explosive is pentaerythritol tetranitrate.

13. A sheet explosive of the composition of claim 1.

References Cited UNITED STATES PATENTS 3,138,501 6/ 1964 Wright 149-92 3,256,214 6/1966 Bluhm 14919X 3,278,350 10/1966 Caldwell et al. 14919X 3,338,764 8/1967 Evans 14919 3,361,689 2/1968 Miegel et al. 149-19X 3,447,980 6/ 1969 Voigt 149-93X BENJAMIN R. PADGETI, Primary Examiner US. Cl. X.R. 

